In surgery, in particular micro-surgery, in the acquisition of biopsy samples, in medical imaging, in the recording of electrical activity from neurons and glia cells, and in therapeutic irradiation of tissue the geometric relationship between the affected tissue, at the one hand, and the surgical instrument, biopsy probe, imaging apparatus or radiation beam, on the other, should be stable. While a patient can be partially or wholly immobilized on a support to prevent him or her from moving during surgery etc., this does not prevent tissues under autonomous control from moving nor does it, for instance, hinder the patient from breathing or ventilating or from moving the eyes.
Methods for coping with such movements are known in the art. They comprise monitoring the changing position, i.e. the movement, of the tissue of interest in respect of an apparatus, such as an apparatus for imaging the tissue, or a radiation source for irradiating it or a device for interacting with the tissue, such as one for biopsy, etc. The apparatus or radiation source or device is displaced by motor means in a mirroring manner in respect of the moving tissue so as to keep its spatial relation to the tissue or its focus on the tissue constant over time. The motor means that effect the displacement are controlled by microprocessor means based on position data acquired by monitoring a movement of the tissue. The methods known in the art thus seek to trace the movement of a tissue as closely as possible and to use the position data acquired in this tracing to control the motor means as fast as possible via microprocessor means.
A problem with the methods known in the art is that they are only responsive to tissue movements, which are often difficult to predict. The time lag between the registration of a tissue movement and the thereon based counter measure controlled by the microprocessor and executed by the motor means taking effect often does not allow an acceptable compensation of such neurally triggered or other self-caused displacement of tissue.
Sources of involuntary body movements include heartbeats, respiration, peristaltic movements of the intestine, and muscular tremor. The movements of various organs and tissues are most often unrelated, that is, not concerted, and often are not uniform. They can interact in a complex manner making physiologically unrelated movements to add to each other or to compensate each other. Most often they cannot be predicted from a mere imaging of the tissue of interest.